div {
    width: 100px;
    height: 100px;
    border: 1px solid red;
    text-align: center;
    line-height: 100px;
}
.big {
    width: 500px;
    height: 500px;
    border: 2px solid blue;
    position: relative;
}
.div1 {
    height: 1000px;
    /* 相对定位 */
    position: relative;
    left: 10px;
    top: 10px;
}
.div2 {
    background-color: #ffc0cb;
    /* 绝对定位 */
    position: absolute;
    left: 0px;
    top: 0px;
}
.div3 {
    height: 1000px;
}
.div4 {
    /* 固定定位 */
    position: fixed;
    top: 0;
    left: 0;
}